In recent years, as image quality and precision in copiers and printers have been higher, requirements for the performance of a toner as a developer have been also even severer, and thus a toner having a smaller particle diameter and a sharper particle size distribution containing no coarse particles has been being demanded.
Further, as a transferring material for copiers and printers, there has been a need for responding to a variety of materials other than common paper, and the toner has been required to exhibit improved transferring properties. Thus, there has been a need for spheroidizing the toner particles.
However, on the other hand, if a toner is spheroidized too much, the cleaning properties of the toner are deteriorated, and thus there are also demands for controlling a degree of sphericity of the toner and for satisfying its transferring properties and cleaning properties at the same time.
With respect to such requirements, one production method in which a degree of sphericity of a toner is controlled is a method in which a surface of a toner is melted and spheroidized by a heat treatment. In the case of spheroidizing a toner by a heat treatment, there is a demand that the shape of a toner is made uniform by suppressing the coalescence of toner particles and uniformly heat-treating the particles during the heat treatment in order to satisfy the transferring properties and cleaning properties of a toner at the same time.
For achieving the above purposes, a heat treating apparatus having a turning mechanism for dispersing a powder which is a raw material and a heating mechanism that heats the dispersed powder raw material from the inside has been proposed (see, PTL 1).
However, in the case of heat-treating a toner in such an apparatus configuration, a flow current of dispersing the raw material and a flow current of heating the raw material are opposite to each other in terms of a turning direction. Therefore, if the amount of a toner to be treated is increased, the toner may be adhered to the ceiling surface and the wall surface of the apparatus by a disturbance in flow current caused in the apparatus, thereby causing a melt-adhesion product in some cases.
With regard to this, it has been proposed to blow cooling air in a slit manner from an upper portion of a side wall of a heat treating chamber in a heat treating apparatus, thereby suppressing adhesion of particles and a turbulent flow to improve productivity (see, PTL 2).
However, in the case of heat-treating a toner in such an apparatus configuration, while a flow current of dispersing a raw material and a flow current of heating a raw material are turning flows, cooling air to be introduced is perpendicular. As a result, a turbulent flow current is generated in the apparatus after all, and a heat treatment with an increased amount of a toner to be treated may cause melt-adhesion or fusion of the toner. Further, in such an apparatus configuration, since the flow current of heating a raw material is cooled by the flow current of dispersing a raw material, an excessive amount of heat must be applied for spheroidizing toner particles. Therefore, an amount of heat that the toner particles receive in the apparatus may vary, so that the toner may not be heat treated uniformly and the toner particles may not be made uniform in terms of the shape in some cases.
In this way, there is room for improvement in a heat treating apparatus for powder particles in order to satisfy transferring properties and cleaning properties of a toner at the same time by efficiently and stably producing a toner which contains no coarse particles and has a uniform shape when spheroidizing a toner by a heat treatment.